Composite conductor



June l0, 1930.

Filed Nov. 27, 1926 F. F. FARNSWORTH COMPOSITE CONDUCTOR Patented June 10, 1930 UNITED STATES PATENT OFFICE FRANK F. FARNSWORTH, OF FLUSHING, NEW YORK, ASSIGNOR T0 BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A'CORPORATION OE NEW YORK COMPOSITE CONDUCTOR v f Application tiled November 27, 1926. Serial No. 151,171.

This invention relates to the construction of signaling conductors and more particularly to the construction of such conductors continuously loaded with magnetic material.

The loading of signaling conductors with magnetic material. to improve the transmission characteristics of signaling circuits is now well known. Certain alloys containing nickel and iron are now beingl used for this purpose. -'l`hcse alloys, when properly heat treated, are peculiarly desirable for loading material by virtue of properties, some ot' which vary when the material is strained, as is incidentally done by changing its form in appling it. to a conductor. lt is, therefore, liest to perform the heat treating operation upon the loaded conductor, but even then certain structural precautions must be taken for best results.

A structural precaution provided in accordance with this invention resides in a p. \\'der-likey separator between the conductor and the loading material, the separator being an electrochemical deposit from a solution of ammoniun'l molybdate converted into a powder by the application ofhcat.

Another feature of the' invention relates to the method of preparing such a loaded conductor which comprises, first depositingr a continuous coating on either the individual strands from which the conductor is to be prepared, the solid or stranded conductor itself, or the unapplied loadingr material in a sufficiently adherent t'orm to remain in place f except when the surface to which it is applied is sharply bent, and then applying the loading material over the conductor. The loaded conductor is then subjected to a heat treatment, which causes the continuous or coherent coating to be converted into a powder-like consistency, and the loading material to acquire desired magnetic properties. Electrodeposit ion is the preferred process for obtaining an adherent coating.

A more detailed description of the inven tion follows and is illustrated in the accompanying drawing in which:

Fig. l illustrates a continuous process for depositing the coating on a single strand;

liig. 2 shows a section of a loaded conductor with a portion cut away to illustrate details of construction; and

Fig. 3 is a cross-sectional view of the conductor of Fig. 2.

Until comparatively recently, iron has been considered to be the only material suitable tor the continuous loading of' a signaling conductor. It has been discovered, however, that material in general more suitable than iron may be produced in the form of alloys. When nickel and iron are alloyed in proper proportions and the alloy is given a proper heat treatment, a material having properties peculiarly suited for continuous loading of signaling conductors is obtained. One alloy7 which is desirable because of its high permeability has a composition comprising TS1/2% nickel and '2U/2% iron. Another magnetic alloy which exhibits very great constancy of permeability under the conditions encountered in signaling circuits comprises nickel, 30% iron and 25% cobalt. However, in order to bring out the desirable qualities of these alloys they must be properly heat treated. For a detailed description of these loading materials, see an article in the Journal of the Franklin Institute, Volume 195, `Number 5, for May, 1923, by Messrs. Arnold and Elmen, entitled Permalloy, an alloy of remarkable magnetic properties, and the copending application of G. lV. Elmen, Serial No. 119,622, tiled June 30, 1926, and which has issued as Patent No. 1,715,646, on June 4, 1929.

lVhen it is attempted to employ these materials either in the form of tape or wire for continuously loading a conductor, difficulties are encountered. Desired qualities which are attainable by proper heat treatment prior to the placing of the material upon the con- 2 l igzeaeea ductor are deleteriously atlfected by the inechanical strains incident to the application process; hence, the finished conductor is heat treated. A suitable heat treatment for obtaining the desired properties ot both the nickel-iron and nickel-iron-cobalt allows comprises heating the alloy to approximately 900O C. after it has been applied to the copper conductor. During such process, a coudition arises which prevents desired magnetic or electrical properties ot the loading material, as for example, high attainable permeability, from being attained.

The present invention is one of a series of inventions which have been made with the object of avoiding this condition.

rl"he preferred process ot' continuously forming by electrodeposition a coherent coating on a conductor is shown in F ig. l, in which the conductor l0, to be coated, is supplied from a rotatable reel ll. A brake lever l2 engaging the reel and a tension spring 13 regulate the rotation of the rcel 11. The conductor l0 enters a hot alkali bath M, contained in a metallic tank l5, guided by a plurality ot iron pulleys or rollers 16.

rlhe alkali bath consists of approximately one pound of caustic soda to each gallon of Water to form a cleansing solution to remove foreign substances from the metallic concluetor 10. rlhe conductor is drawn through a Water bath i7 for Washing after leaving the alkali bath and a Wiper l-l surrounds the conductor adjacent the end of the alkali bath to prevent an excess of alkali solution from being carried into the Water bath. The rollers 18 engaging the conductor during the Washing operation are preferably oi' brass or bronze to prevent injurious oxides being rformed atthese points and being applied to the portion oit' the conductor in contact with the rollers.

rEhe conductor l() is then drawn through the acid dip bath l5), to remove scale and etch the conductor prior to the. coating operation. This bath comprises troni one to tiro pounds` of concentrated hydrochloric acid to each gallon ot ivater but may be a concentrated hydrochloric acid balli. and is preferably contained in a glass or porcelain tank The rollers :2l for this bath are preferably of rubber which is substantially unall'ected by the acid. A 'wiperv 22. also ot' rubber, removes the excess acid solution troni the conductor l0 after it leaves the acid bath. The next bath 23 the same as the bath l?, namely, a clear water bath to rin-te the conductor attcr the acid bath. fr suitable tap 2lmay be positioned over the conductor to supply a constant lion' oil Water to Wash the conductor.

The conductor lt) then enters the coating bath which is contained in a lead-lined tank 2li. This bath consists of a solution of annnonium molybdate formed by dissolvingl niolybdic acid in sufficient ammonium hydroxide to form a clear solution of the tormula ("rllldgli/OO.i and diluting With ivater to the proper strength. Solutions having from 2% to (3% of the molybdic acid have been found suitable as electrolytes for 'l'orniing the inolybdatc scale coatings. This bath is .maintained at a temperature ot from GOO to TUO (l. b v a heater enclosed in an oil lilled glass tube 27, or any suitable type of immersion heater. The heater is connected to a source of current, such as a battery 2S. rlhe current supply is controlled by a variable resistance 29. A copper or bronze roller l0 is supported adjacent to the entrance of the coating bath, to torni the cathode contact for the conductor l0. he cathode Contact rollei- 30 and the lead lining of the tank 6 which acts as the anode of the bath are connected to a source of current 31 through an amincter 32 and a variable resistance 33. 'l`he current density of the solution is maintained at the required values to form an adherent coating on the conductor l0 which is the cathode ot' the electrolytic bath, by Virtue of its contact engagement with the roller 30. The values of thecurrent density of the bath which have been found desirable are a proximately l() to l5 amperes per square oot of anode surface. Suitable porcelain or glass rollers Il-l guide the conductor l0 through the electrolytic bath.

The coherent coating which is deposited on the conductor l0 as it passes through the bath, is probably an oxide or a molybdate of the metal to be coated, or it may be a mixture of molybdate and oxide. Vhatever the composition of the coating, a reasonably uniform thickness of an adherent metallic scale is formed on the conductor since the coating becomes fairly nonconducting alter a certain thickness has been formed and terminates the `forming process. After the coated conductor leaves the bath, a Wiper 35 removes the excess solution from the conductor to prevent the pollution ot the Washing bath lili through which the 'coated conductor is guided by the brass rollers 37. Auxiliary washing streams oi water are supplied-from taps 35 arranged so that the Water iiou's over the conductor and into the final washingl tank. il. drying Wiper 3G surrounds the coiuluctor alter it leaves the Washing bath 3G and the conductor is Wound on a take-up reel 3l). This arrangement forms a continuous process for treating and coating the metallic conductor to 'form by electro-deposition a coherentA coating, tnobably ot' molybdate, on the surface thereof.

Referring to Figs. 2 and il, a plurality ol' llat conducting strands -l-Orwhich have applied thereto the molybdate coating -ll` are. helically Wrapped on a solid conducting'core al, and a magnetic tape l2 is applied over the conducting strands to forni a composite contlf) n nt

treating and depositing the coating on a` single strand or conductor, it is apparent that a large number of strands or conductors may pass through the process sirmlltancously. Furthermore, the coating may be deposited on a solid conductor, such as the core 41 and the magnetic tape 42 applied directly to the coating on the solid conductor.

It is to be understood that the expression molybdate scale, where used in the specification and claims, is not to be taken as a definite representation ofthe chemical composition of the scale. Such expression is used merely to define the deposit produced under certain conditions and assumed to be a metallic molybdate.

A possible explanation of the deleterious effects produced by the heat treating process is that unless precautions are taken, adhesion takes place between the copper ,conductor and the loading material. In the process of heating the loaded conductor at about 000o C. the copper expands considerably more than the surrounding loading material and when' there is not sufficient slack in the loading material very close contact is established between the two, either in the furnace or just after the conductor enters the cooling chamber. Contraction of the loading layer vis rapid in the latter stage of the heat treatment due to the cooling medium coming in contact directly with this layer. Due to the increased molecular activity at the elevated f temperature of 900 C. diffusion between the two metals appears to be established and welding or adhesion takes place over portions at least of the Contact surfaces. Upon cooling of the copper conductor the latter' tends to draw away from the magnetic loading material and since this material partially adheres to the copper, ,stresses are set up which are great enough to deletcriously affect properties of the loading material.

While the invention has been particularly described with reference to loaded signaling conductors it may be employed in other types of composite strands which are subjected to high temperature conditions and in which contact between the individual strands during the heating or subsequent cooling gives rise to deleterious etlects.

1. A signaling conductor comprising a plurality ot' component strands in close contact,

and a thin layer of molybdate powder between the component strands.

2. A signaling conductor comprising a plurality of component strands in close contact, and a n electrodeposited coating of molybdate on at least one of said strands.

3. A- composite signaling conductor comprising a central copper strand, a magnetic strand wound thereon, said magnetic strand being subject to adhesion to said central strand during heat treatment, and a thin layer of loosely adherent metallic -molylodate between said strands.

4. A loaded signaling conductor comprising a conduct-ing strand, a magnetic loading material wrapped about said strand, said loading material requiring heat treatment to develop high permeability therein and the permeability being sensitive to strain, and a coating of molybdate separating the loading material from said conducting strand.

' 5. A loaded signaling conductor comprising a central conductor, a plurality of conducting strands spirally applied to said conductor, a layer of magnetic loading material surrounding said strands, said signaling conductor being subjected to heat treatment to increase the permeability ot' Said. loading material, and an electrodeposited coating of molybdate scale between said loading material and conducting strand.

6. A continuously loaded signaling conductor compri-sing a conducting strand, a magnetic strand, and an adhering coating on one of said strands to separate it from the other of said strands, said coating being a high melting point, metallic composition of the type which is obtained by electrodeposi- Vtion from an ammoniacal solution of a metallic acid which may be transformed into a powder when heated below fusing.

7. The method of separating two conducting bodies with an insulating layer comprisingdepositing a molybdate scale adherently to one of the conducting bodies, and then placing said bodies in close proximity to each other.

8. The method of producing a composite metallic strand free from adhesion between the component strands during heattreatment, which comprises electrolytically producing a molybdate deposit on one of the component strands, and superimposing another strand on said coated strand.

9. The method ot producing a composite strand free from adhesion between the component strands during heat treatment vwhich comprises passing one of the component strands through a solution of ammonium molybdate, lorming electrolytically from said solution a coherent metallic coating on said strand and superimposing another strand on said coated strand.l

1t). The method of producing a signaling conductor free from adhesion between the fifi iframes separate strands et said conductor during an ammoniacal solution of molybdic acid,

heat treatment, which comprises coating one of the strands electroliticall;v with a molybdate on the metal of said strand. and winding anotheiI 'strand in contact with said coated strand.

1l. rThe method ot producing a signaling conductor comprising a conducting strand and a magnetic strand, said strands being subject to adhesion during heat treatment, which consists in producing a molybdate coating on the conducting strand by electrochemical deposition, and winding the magnetic strand in Contact with said conducting strand.

l2. The method of providing a non-coherent separator between adjacent strands of a composite signaling conductor, which comprises electrolvtica'll)v depositing on one of said strands from an ammoniacal solution a coherent coating of a metallic composition said coating having a high melting point, building np said conductor to include said adjacent strands, and then breaking up said coating by applying heat to said conductor.

13. The method of providing a powderlike, refractory separator between adjacent strands of a composite signaling conductor, which comprises electrodepositing trom an ammoniacal solution a metallic compound on one of said strands, building np the conductor from said strands` and then heating the compound to a temperature below insing.

14. The method of producing a signaling conductor comprising a conducting strand and a magnetic strand, said strands being subject to adhesion during heat treatment, which consists in electrolyticallyv producing a molybdate deposit on the conducting strand, winding the magnetic strand in contact with said conducting strand` and heating said signaling conductor to improve the properties of said magnetic material, said molybdate deposit being reduced to a looselyY adherent powder.

l5. The method of loading a signaling conductor with magnetic material which requires heat treatment to improif'e its magnetic properties which comprises, forming a layer of molybdate on the conductor, and Wrapping the magnetic material in contact with said molybdate layer.

lo. The method oi'I loading a signaling conductor with magnetic material which requires heat treatment to increase the electrical characteristics of the magnetic material, which consists in electrolytically depositing a molyhdate coating on the conducting strand, wrapping said strand spil-ally on a central strand, and wrapping a layer of magnetic loading material about said depositing strand.

17. The method of loading a signaling condoctor with a magnetic material whiclircomprises passing the conducting core through forming electrolyuically in said solution a molybdate coating on said core, applying the magnetic material about said coating and heating the loaded conductor to improre one of its properties and to reduce said coating to a powder-like condition.

n Witness whereof, l hereunto subscribe my name this 24th day of November, A. D.

FRANK F. iraRNSWoRT-i. 

